This invention relates to radar systems and in particular to an apparatus for testing the performance of a radar system by monitoring the radar transmitted power, the receiver sensitivity and tuning.
Such a radar performance monitor is described in U.S. Pat. No. 4,145,692 to David G. Armstrong et al and assigned to the present assignee. As stated therein it is generally not difficult to determine whether a landbased radar is operating properly or not; there are small fixed targets whose appearance on the display is known and remembered, and if they fade or disappear, the radar is losing sensitivity or malfunctioning. Marine radars, on the other hand, are generally used far out at sea where there may normally be no targets and a partial or complete loss of radar performance may not be apparent to the operator. Some countries require by law that the marine radars be equipped with some sort of performance monitor and this requirement will become more prevalent. Such monitors are particularly useful with the kind of radar which performs automatic tracking and can operate in a night watch mode in which it is unattended by an operator. If the radar detects and tracks an object which may be on a collision course, an alarm is sounded. The alarm is also sounded if the performance monitor detects a radar malfunction alerting the operator that automatic tracking is not being reliably provided.
An echo box has been used in the past for monitoring radar performance; this has been generally expensive and not very satisfactory. It usually requires direct coupling into the radar's RF transmission line. It is limited in the range at which it can produce a response on the radar's display. It commonly requires a mechanical, motor-driven, tuning device.
The invention described in U.S. Pat. No. 4,145,962 not only provided a test pattern for monitoring the radar's transmitted power level and receiver sensitivity but also indicated the proper tuning of the receiver to the transmitter frequency, and therefore, was used as an aid in tuning a manually tunable radar receiver. However, that performance monitor had a local oscillator controlled by an AFC loop which was complicated and required many parts resulting in relatively high costs and low reliability as compared with the performance monitor of the present invention.